Abstract
Key messageQTL-M and QTL-E enhance soybean resistance to insects. Pyramiding these QTLs withcry1Ac increases protection against Bt-tolerant pests, presenting an opportunity to effectively deploy Bt with host–plant resistance genes.Plant resistance to leaf-chewing insects minimizes the need for insecticide applications, reducing crop production costs and pesticide concerns. In soybean [Glycine max (L.) Merr.], resistance to a broad range of leaf-chewing insects is found in PI 229358 and PI 227687. PI 229358’s resistance is conferred by three quantitative trait loci (QTLs): M, G, and H. PI 227687’s resistance is conferred by QTL-E. The letters indicate the soybean Linkage groups (LGs) on which the QTLs are located. This study aimed to determine if pyramiding PI 229358 and PI 227687 QTLs would enhance soybean resistance to leaf-chewing insects, and if pyramiding these QTLs with Bt (cry1Ac) enhances resistance against Bt-tolerant pests. The near-isogenic lines (NILs): BenningME, BenningMGHE, and BenningME+cry1Ac were developed. BenningME and BenningMGHE were evaluated in detached-leaf and greenhouse assays with soybean looper [SBL, Chrysodeixis includens (Walker)], corn earworm [CEW, Helicoverpa zea (Boddie)], fall armyworm [FAW, Spodoptera frugiperda (J.E. Smith)], and velvetbean caterpillar [VBC, Anticarsia gemmatalis (Hübner)]; and in field-cage assays with SBL. BenningME+cry1Ac was tested in detached-leaf assays against SBL, VBC, and Southern armyworm [SAW, Spodoptera eridania (Cramer)]. In the detached-leaf assay, BenningME showed the strongest antibiosis against CEW, FAW, and VBC. In field-cage conditions, BenningME and BenningMGHE suffered 61 % less defoliation than Benning. BenningME+cry1Ac was more resistant than BenningME and Benningcry1Ac against SBL and SAW. Agriculturally relevant levels of resistance in soybean can be achieved with just two loci, QTL-M and QTL-E. ME+cry1Ac could present an opportunity to protect the durability of Bt genes in elite soybean cultivars. These results should assist the development of effective pest management strategies, and sustainable deployment of Bt genes in soybean.
Highlights
The production of soybean [Glycine max (L.) Merr], one of the world’s primary sources of vegetable oil and proteinTheor Appl Genet (2016) 129:703–715(Wilcox 2004), is often limited by pests
The efficient use of insecticide applications depends on economic thresholds (ETs), which are based on percent of defoliation and are used to monitor insect populations to prevent them from reaching levels that may cause economic losses
The pyramided near-isogenic lines (NILs) BenningME, BenningMGH, and BenningMGHE were the least defoliated across the four experiments
Summary
The production of soybean [Glycine max (L.) Merr], one of the world’s primary sources of vegetable oil and proteinTheor Appl Genet (2016) 129:703–715(Wilcox 2004), is often limited by pests. In the USA, the insect pests causing the most impact are: corn earworm [Helicoverpa zea (Boddie)], soybean looper [Chrysodeixis includens (Walker)], velvetbean caterpillar [Anticarsia gemmatalis (Hübner)], bean leaf beetle, [Cerotoma trifurcata (Forster)], green stink bug [Chinavia hilaris (Say)], and southern stink bug [Nezara viridula (L)] (Boethel 2004). The corn earworm (CEW), soybean looper (SBL), velvetbean caterpillar (VBC), and bean leaf beetle are chewing insects capable of defoliating plants entirely. The efficient use of insecticide applications depends on economic thresholds (ETs), which are based on percent of defoliation and are used to monitor insect populations to prevent them from reaching levels that may cause economic losses. The suggested ETs for leaf-chewing insects in soybean are 35 % defoliation during the vegetative stages and 20 % defoliation during the reproductive stages (Heatherly 2014)
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